Preparation of Strontium Barium Niobate by Sol–Gel Method

Crack-free SBN (Sr_xBa_1-xNb₂O₆) thin films have been prepared by a sol–gel method with metal alkoxides. A homogeneous and stable precursor solution was obtained from Sr and Ba metal and Nb(OEt)₅ in ethanol with a key additive of ethoxyethanol. SBN (where x = 0.5) powder crystallized to orthorhombic phase at 700°C, and then transformed completely to tetragonal phase at 1200°C. The formation of tetragonal SBN was observed on sapphire (R) substrates at 700°C, whereas the tetragonal phase began to appear in the powders at 1000°C. SBN films with highly preferred orientation were successfully synthesized on MgO (100) substrates at 670°C.     

Electro-optic properties of c-axis oriented LiNbO3 films grown on Si(1 0 0) substrate

We developed a spectroscopic–ellipsometric approach to evaluate the electro-optic coefficient of highly c-axis oriented LiNbO₃ films on an Si(1 0 0) substrate grown by electron cyclotron resonance plasma sputtering. Applying an electric field between the TiN transparent top electrode and Si substrate, the interference fringe appearing in the tan Ψ spectrum was slightly modulated by phase retardation in the wavelength domain. The change in effective wavelength was converted to refractive index change, yielding dispersion in the Pockels coefficient (r₃₃) between 0.3 and 0.8 μm. At 633 nm, we obtained an r₃₃ that was 57% of the bulk LN crystal value.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Fabrication of Transparent Yttria Ceramics at Low Temperature Using Carbonate-Derived Powder

A new preparation method for a highly sinterable yttria powder has been developed, the resultant powder characterized, and its sinterability studied. As a precursor of the yttria powder, a fine and needle-shaped yttrium carbonate was prepared by a precipitation and aging method. A fine and low-agglomeration yttria powder was obtained by calcining the carbonate precursor at 1100°C. The primary crystallites measured ∼0.1 μm and weakly agglomerated to a size of ∼0.3 μm. The powder had a very high sinterability, so that the powder compact could be sintered to transparency by normal sintering under vacuum without additives at low temperatures, over 1600°C. The sintered transparent ceramics exhibited a homogeneous microstructure with no abnormal grain growth.     

Gas-Sensing Properties of Spinodally Decomposed (Ti,Sn)O2 Thin Films

The gas-sensing properties of spinodally decomposed (Ti,Sn)O₂ thin films on sapphire substrates were investigated for CO, C₃H₈, and C₂H₅OH, and hydrogen gases at a temperature of 500°C. The variation in the d -spacing of the (101) plane of (Ti_0.5Sn_0.5)O₂ films showed behavior that was typical of spinodal decomposition during annealing at a temperature of 900°C. Transmission electron micrographs of the spinodally decomposed (Ti,Sn)O₂ films on sapphire (0112) substrates revealed the characteristic modulated structure. The modulated lamella microstructure consisted of TiO₂- and SnO₂-rich regions at intervals of ∼10 nm. The films were very sensitive to hydrogen gas and revealed anisotropic electrical conduction that was influenced by the modulated microstructure, which is characteristic of spinodal decomposition.     

Effect of arrangement of pillar array of aligned carbon nanotube bundles on its field-emission characteristic

We investigated the properties of field emission from a pillar array of aligned carbon nanotube (CNT) bundles, which were fabricated on a Si substrate by thermal chemical vapor deposition. To explore the influence of the pillar arrangement on its field emission, the ratio of interpillar distance (R) to pillar height (H), R/H, was investigated as a function of H by changing H while maintaining R at 100 μm. The most-enhanced field concentration was obtained at R/H ∼ 6, although we previously reported that the optimal configuration of pillars for R = 250 μm was a ratio of R/H = 2. These results show that the optimal R/H for greatest field emission from the CNT pillar array is dependent on R.     

Potassium Lithium Niobate Films Derived from Aqueous Precursor Solution

Potassium lithium niobate (KLN) films, which were prepared using an aqueous precursor solution, were characterized in terms of crystallinity, morphology, and electrical properties; 1.0 μm thick KLN films free from cracks and pores could be prepared on MgO(100), Pt(100)/MgO(100), and Pt(111)/Ti/SiO₂/Si substrates by multiple coating and heating at 700°C. The films were composed of compact grains and had sintered textures. The films crystallized with (310) and (540) preferred orientations on MgO(100) and Pt(100)/MgO(100) substrates. The KLN film prepared on Pt(100)/MgO(100) substrate had ɛ'= 136 and tan δ= 0.026 at 1 kHz.     

Simple purification and selective enrichment of metallic SWCNTs produced using the arc-discharge method

Purified single-walled carbon nanotubes (SWCNTs) were produced using the arc-discharge method with a combination of air oxidation and dispersion–centrifugation processes in a tetrahydrofuran solution containing an amine as a dispersant. Subsequently, SWCNT samples were analyzed using thermo gravimetric analysis, vis-near infrared absorption spectroscopy, scanning electron microscopy, and Raman spectroscopy. Results revealed that metallic SWCNTs were enriched in a supernatant through the dispersion–centrifugation process.     

Lithium ion cell safety

The safety characteristics of recent commercial lithium ion cells are examined in relation to their use for cellular phones. These are prismatic cells with an aluminum cell housing (can) and a 500–600 mA h capacity. They have one of two types of 4-V class cathodes, lithium cobalt oxide (LiCoO₂) or lithium manganese oxide (LiMn₂O₄). This report provides results of the safety tests that we performed on lithium ion cells and outlines our views regarding their safety.